Two known formats for transporting data in communications networks are circuit-switched and packet-switched. Circuit-switched networks are more reliable than packet-switched networks for real-time applications and those requiring a guaranteed quality of service, such as voice and video, whereas packet-switched networks are more efficient at transmitting data, including email and internet data exchange applications. Circuit switching is used in traditional voice telephone technologies. Packet switching has emerged as the preferred method for data technologies, such as computer-to-computer communications.
Resources are dedicated for circuit-switched calls when the call is set up and remain assigned until the call is completed. Circuit-switched calls have end-to-end resources with a fixed bandwidth allocated for the entire call and typically do not need information, such as headers, above Layer 1. Circuit-switched calls tend to be more expensive because of dedicated bandwidth. Typically, circuit-switched resources are required even during silent periods when no information is being exchanged.
Resources, including bandwidth, are not dedicated for packet-switched calls. The information content of packet-switched calls is divided into packets that are routed based on their destination and repackaged at intermediate network elements for transmission. Packet-switched calls require sending of information, such as headers, above Layer 1 to determine the destination and/or path for the data. When the network becomes overburdened, packets may be buffered in network elements and/or dropped. Buffering causes transmission delays, possible receipt of packets out of order, and packet loss and results in deterioration of quality in real-time applications. For non-real-time applications, packets received out of order may be reordered by a higher layer protocol, and retransmission of missing packets upon request is employed by standard higher layer packet protocols. For non-real-time applications, delays due to retransmission and reordering of packets are acceptable, but such delays may severely affect the quality of service for real-time applications. Packet-switched calls cannot provide a guaranteed level of quality for real-time applications, and the quality deteriorates as traffic in the network increases. Packet-switched calls tend to be less expensive than circuit-switched calls because of sharing of available resources and bandwidth.
Today's networks are designed either exclusively for circuit switching or exclusively for packet switching. A network service provider typically builds two separate networks, a circuit-switched network for voice calls and a packet-switched network for data calls. Thus, e-mail is sent over the packet-switched network, because sending an email over a circuit switched network is wasteful, and voice calls are sent over the circuit-switched network, because sending a voice call over a packet-switched network results in poor quality of service, marked by distortions or gaps. Supporting and operating two separate networks increases the cost and complexity of today's networks.
Multi-media transmissions over today's networks also have drawbacks. When circuit-switched networks are utilized for multi-media calls, bandwidth is wasted when resources are assigned to accommodate worst case conditions, such as video. Thus, when data is transmitted, much unused bandwidth results, causing circuit-switched calls to be expensive. When packet-switched networks are utilized for multi-media calls, real-time applications such as voice and especially video suffer from missing data, and transmissions tend to have longer delays and poorer quality. In addition, with either network, resources are typically assigned at a fixed bandwidth, and when one part or session of a multi-media call exceeds its bandwidth, that part is either cut off or takes over resources for another part of the call, causing that part of the call to experience reduced quality.
Accordingly, there is a need for a better method and apparatus to utilize circuit-switched and packet-switched technologies, and additionally a better way to handle multi-media calls is needed.